High-purity nanoscale lithium sulfide and a method for preparing the same

Abstract

The application provides high-purity nanometer lithium sulfide and a preparation method thereof, and belongs to the technical field of solid-state lithium battery materials. The method can comprise the following steps: material purification, nanometer wet grinding, homogeneous reaction and ball milling, so that the high-purity nanometer lithium sulfide product is obtained. The high-purity nanometer lithium sulfide and the preparation method thereof have the advantages of high product purity, superior performance, simple operation and good social and economic benefits.

Description

Technical Field

[0001] This invention relates to a high-purity nano-scale lithium sulfide and its preparation method, belonging to the field of solid-state lithium battery material technology. Background Technology

[0002] In recent years, the new energy vehicle industry has flourished, but issues such as range anxiety, charging time, and safety have hindered further market share expansion. Lithium-sulfur batteries and all-solid-state batteries are considered among the most promising directions in next-generation battery technology due to their high energy density. Lithium sulfide, which can serve as both the active cathode material in lithium-sulfur batteries and a key raw material for synthesizing solid electrolytes, has become a star material in the rechargeable battery field. According to an in-depth report on solid-state lithium batteries, based on the existing lithium battery market size, the potential market size for lithium sulfide used in solid-state batteries may reach tens of billions of yuan, indicating a very promising market outlook.

[0003] Lithium sulfide is a crucial component of sulfide-based solid electrolytes (SEEs), influencing the ionic conductivity of SEEs and being a major factor determining the performance of all-solid-state batteries. Therefore, the quality requirements for lithium sulfide materials are becoming increasingly stringent. Recent studies have also shown that lithium sulfide particle size significantly impacts SEE performance. The international journal *NanoLett* reported that sulfide electrolytes with particle sizes smaller than 1 μm are more stable in contact with metallic lithium, mitigating the chemimechanical failure (CFM) of SEEs. A recent study published in the *Journal of Energy Chemistry* by Tianjin University found that micron-sized lithium sulfide used as the cathode in lithium-sulfur batteries lacks electrochemical activity and is susceptible to mechanical damage from volume fluctuations. In contrast, nano-sized lithium sulfide overcomes these problems. The high specific surface area provided by nano-sized lithium sulfide promotes the lithiation / release process, resulting in improved performance through reduced electro-ionic resistance, increased capacity, and reduced mechanical stress associated with volume changes. Furthermore, industry experts have suggested that magnetic materials can affect SEE performance; therefore, a demagnetization process should be incorporated into the subsequent preparation of lithium sulfide to further reduce the content of magnetic materials.

[0004] CN112678781A discloses a method for preparing lithium sulfide. The specific steps of the method are as follows: Grinding and mixing: Sulfur source and lithium source are mixed and ground, and hydrazine hydrate is added during grinding. After the addition is completed, the grinding is stopped to obtain the reaction material; wherein, the sulfur source is sulfur powder, lithium thiosulfate, or lithium sulfite; the lithium source is lithium hydroxide, lithium thiosulfate, or lithium sulfite; Vacuum defoaming: The reaction material is placed in a vacuum defoaming tank, and a vacuum is drawn. After the bubbles are eliminated, the vacuum state is maintained for 1-4 hours, and then the pressure is changed to normal pressure to obtain a lithium sulfide solution; Drying: The lithium sulfide solution is dried to obtain lithium sulfide. This method has the following drawbacks: it cannot produce high-purity (purity > 99.99%) lithium sulfide products. At the same time, due to the large amount of water in the reaction system, the lithium sulfide product exhibits severe agglomeration and large particle size. In addition, the process requires a vacuum defoaming step, which places strict requirements on the sealing of the reactor, making large-scale production difficult. Summary of the Invention

[0005] The technical problem solved by this invention is to provide a method for preparing high-purity nano-sized lithium sulfide.

[0006] A method for preparing high-purity nano-sized lithium sulfide includes the following steps:

[0007] a. Material purification

[0008] Purification of reducing agent: Take hydrazine hydrate, anhydrous hydrazine and / or hydroxylamine reducing agent for purification, and obtain high-purity reducing agent after removing impurities for later use;

[0009] Lithium source purification: The lithium source is purified to obtain a high-purity lithium source, wherein the lithium source is battery-grade lithium hydroxide monohydrate, anhydrous lithium hydroxide, high-purity lithium oxide and / or battery-grade lithium carbonate;

[0010] b. Nanoscale wet milling: Take the high-purity reducing agent and high-purity lithium source obtained in step a at a molar ratio of 1:1 to 3, mix them evenly, and obtain a high-purity lithium source slurry with nanoscale particles and uniform dispersion.

[0011] c. Homogeneous reaction: Dissolve high-purity sulfur powder in the high-purity reducing agent obtained in step a to obtain sulfur-containing slurry; add the sulfur-containing slurry and the high-purity lithium source slurry obtained in step b to the reaction vessel simultaneously according to the chemical reaction stoichiometric ratio and mix them. Under the protection of an inert atmosphere, react and dry to obtain high-purity lithium sulfide with a small amount of adhesion.

[0012] d. Ball milling: The high-purity lithium sulfide with a small amount of agglomeration obtained in step c is ball milled to obtain a uniformly dispersed nano-sized high-purity lithium sulfide product.

[0013] In step a,

[0014] When the lithium source is battery-grade lithium hydroxide monohydrate or anhydrous lithium hydroxide, the lithium source is dissolved in high-purity water to prepare a lithium salt solution, which is then dried and heated to decompose, to obtain anhydrous lithium hydroxide with a water content of <5%.

[0015] When the lithium source is battery-grade lithium carbonate, it is purified by carbonization decomposition.

[0016] When the lithium source is high-purity lithium oxide, purification is not required;

[0017] The lithium source mentioned in step a, if battery-grade lithium hydroxide monohydrate or anhydrous lithium hydroxide is used as raw material, then the concentration of the lithium salt solution is Li2O: 60-80 g / L, and the drying method is vacuum low-temperature drying at a temperature of 75-90℃; if battery-grade lithium carbonate is used as raw material, then water is added to prepare a slurry, and then it is purified again by carbonization decomposition; if high-purity lithium oxide is used as raw material, no purification is required.

[0018] In step a, when the high-purity lithium source is battery-grade lithium hydroxide monohydrate, larger-particle-size lithium hydroxide is heated to below its melting point temperature under a vacuum or inert gas atmosphere, and an inert gas is passed through it until the residual water of crystallization content of the resulting lithium source is less than 5% by weight, thus obtaining a dehydrated high-purity lithium source. This operation can obtain a lithium source with a residual water of crystallization content of less than 5% by weight by controlling the drying temperature, with the aim of improving reactivity and reducing moisture introduction; wherein the inert atmosphere is a nitrogen atmosphere, an argon atmosphere, a hydrogen-argon mixed atmosphere, or other atmosphere; and the heating temperature is 200–450°C.

[0019] In step b, nano-wet milling refers to a method of crushing and mixing materials by utilizing the impact of falling grinding media (such as zirconia balls or steel balls) and the grinding action between the grinding media and the inner wall of the mill.

[0020] The mixing method in step b is as follows: wet grinding with a ball mill for 1 to 8 hours at a speed of 300 to 600 rpm.

[0021] In step c, when the reducing agent is hydrazine hydrate and / or anhydrous hydrazine, high-purity sulfur powder is mixed with it at a molar ratio of 1:1 to 3 to prepare a sulfur-containing solution; when the reducing agent is hydroxylamine, high-purity sulfur powder and hydroxylamine are mixed at a molar ratio of 1:2 to 4 to prepare a sulfur-containing solution; the molar ratio of high-purity lithium source slurry to sulfur-containing solution is Li2O:S = 1:1 to 3.

[0022] In step c, the reaction occurs first at a low temperature and then at an increased temperature. The reaction conditions at the low temperature are: a stirring speed of 100–300 rpm, a high shear dispersion device speed of 2000–5000 r / min, a temperature of 70–150°C, and a time of 1–3 h. The reaction conditions at the increased temperature are: a stirring speed of 300–500 rpm, a temperature of 200–450°C, and a time of 1–3 h.

[0023] In step d, the ball milling speed is 300-600 rpm and the ball milling time is 1-8 hours.

[0024] In this process, at least one demagnetization is performed in any of steps a, b, c, and d to reduce the magnetic material to less than 50 ppb; the magnetic field strength for demagnetization is 8000–12000 GS.

[0025] The second technical problem solved by the present invention is to provide high-purity nano-sized lithium sulfide prepared by the above-mentioned method for preparing high-purity nano-sized lithium sulfide.

[0026] Preferably, the high-purity nano-grade lithium sulfide product has a particle size of <1000nm, a purity of ≥99.99%, and a magnetic content of <50ppb.

[0027] The third technical problem solved by this invention is to provide the application of the above-mentioned high-purity nano-sized lithium sulfide in solid-state batteries.

[0028] Preferably, the solid-state battery is a lithium-sulfur battery.

[0029] The beneficial effects of this invention are:

[0030] 1. The present invention provides a high-purity nano-grade lithium sulfide and its preparation method, which introduces a demagnetization process to reduce the content of magnetic materials, improve the purity and performance of the material, and eliminates the vacuum defoaming step, reducing the sealing requirements of the equipment, thus having good economic benefits.

[0031] 2. The present invention provides a high-purity nano-grade lithium sulfide and its preparation method. The material is pre-nano-sized by wet milling, and then supplemented by a high-shear disperser. By controlling the process parameters, the resulting product particles reach the nano-scale in the first stage, and the material is purified twice to achieve a purity of 4N grade. Attached Figure Description

[0032] Figure 1 This is a scanning electron microscope image of the product obtained by the preparation method of high-purity nano-sized lithium sulfide according to the present invention.

[0033] Figure 2 The image shown is the XRD pattern of the product obtained by the preparation method of high-purity nano-sized lithium sulfide according to the present invention. Detailed Implementation

[0034] The embodiments of the present invention will be described in detail below with reference to specific examples. However, those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the embodiments, conventional conditions apply.

[0035] Example 1

[0036] (1) Material purification: In a fume hood, take a 500mL bottle of commercially available anhydrous hydrazine (hydrazine) and perform vacuum distillation purification to obtain high-purity hydrazine for later use; weigh 500g of battery-grade lithium hydroxide monohydrate and dissolve it in high-purity water to prepare a lithium solution with a Li2O concentration of 60g / L. After evaporation and centrifugation, the resulting wet material is dried in a vacuum at 75℃ for 1h to obtain high-purity lithium hydroxide monohydrate raw material.

[0037] (2) Material dehydration: The high-purity lithium hydroxide monohydrate raw material obtained in step (1) is heated to 200°C under a nitrogen protective atmosphere until an anhydrous lithium hydroxide raw material with a water content of <5% is formed.

[0038] (3) Nanoscale wet milling: Add anhydrous hydrazine solution to a ball mill jar with a molar ratio of Li2O: anhydrous hydrazine = 1:1. Mill the mixture in a ball mill at 300 rpm for 8 hours to obtain nanoscale anhydrous lithium hydroxide slurry.

[0039] (4) Homogeneous reaction: High-purity sulfur powder and anhydrous hydrazine were mixed in a molar ratio of 1:1 to prepare a sulfur-containing slurry for later use. The sulfur-containing slurry and lithium hydroxide slurry were simultaneously added dropwise to a reactor equipped with an anchor-type stirring impeller and a high-shear disperser via a peristaltic pump. The molar ratio of the added materials was Li2O:S = 1:1. Under the protection of an inert atmosphere, the high-shear emulsifying disperser was turned on and the speed was set to 2000 r / min. At the same time, the stirring was turned on at 100 r / min. After reacting at 70°C for 3 hours, the temperature was increased to 450°C and the stirring speed was increased to 300 r / min. The high-shear disperser was turned off and dried for 1 hour to obtain slightly agglomerated primary particles of nano-sized high-purity lithium sulfide.

[0040] (5) Ball milling: The adhesive material is put into a ball mill and milled at a speed of 300 r / min for 5 hours to obtain high-purity nano-grade lithium sulfide.

[0041] (6) Demagnetization: The ball-milled high-purity lithium sulfide was fed into an electromagnetic demagnetizer for demagnetization. The magnetic field strength was set to 8000 GS, yielding a high-purity lithium sulfide product with a magnetic content of less than 50 ppb. SEM and XRD patterns of the obtained product are shown below. Figure 1 , Figure 2 As shown.

[0042] Example 2

[0043] (1) Material purification: In a fume hood, take a 500mL bottle of commercially available anhydrous hydrazine (hydrazine) and perform vacuum distillation purification to obtain high-purity hydrazine for later use; weigh 500g of anhydrous lithium hydroxide and dissolve it in high-purity water to prepare a lithium solution with a Li2O concentration of 70g / L. After evaporation and centrifugation, the resulting wet material is dried in a vacuum at 80℃ for 1h to obtain high-purity lithium hydroxide monohydrate raw material.

[0044] (2) Material dehydration: The high-purity lithium hydroxide monohydrate raw material obtained in step (1) is heated to 300°C under a nitrogen protective atmosphere until an anhydrous lithium hydroxide raw material with a water content of <5% is formed.

[0045] (3) Nanoscale wet milling: Add anhydrous hydrazine solution to a ball mill jar with a molar ratio of Li2O: anhydrous hydrazine = 1:2. Mill the mixture in a ball mill at 600 rpm for 1 hour to obtain a uniformly dispersed nanoscale anhydrous lithium hydroxide slurry.

[0046] (4) Homogeneous reaction: High-purity sulfur powder and anhydrous hydrazine were mixed in a molar ratio of 1:1 to prepare a sulfur-containing slurry for later use. The sulfur-containing slurry and lithium hydroxide slurry were simultaneously added dropwise to a reactor equipped with an anchor-type stirring impeller and a high-shear disperser via a peristaltic pump. The molar ratio of the added materials was Li2O:S = 1:2. Under the protection of an inert atmosphere, the high-shear emulsifying disperser was turned on and the speed was set to 5000 r / min. At the same time, the stirring was turned on at 300 r / min. After reacting at 150°C for 1 hour, the temperature was increased to 200°C and the stirring speed was increased to 500 r / min. The high-shear disperser was turned off and dried for 3 hours to obtain slightly agglomerated primary particles of nano-sized high-purity lithium sulfide.

[0047] (5) Ball milling: The adhesive material is put into a ball mill and milled at a speed of 600 r / min for 1 h to obtain high-purity nano-grade lithium sulfide.

[0048] (6) Demagnetization: The high-purity lithium sulfide after ball milling is fed into an electromagnetic demagnetizer for demagnetization. The magnetic field strength is set to 12000GS to obtain a high-purity lithium sulfide product with magnetic material less than 50ppb. The product purity data is shown in Table 1.

[0049] Example 3

[0050] (1) Material purification: In a fume hood, take a 500mL bottle of commercially available anhydrous hydrazine (hydrazine) and perform vacuum distillation purification to obtain high-purity hydrazine for later use; weigh 500g of anhydrous lithium hydroxide and dissolve it in high-purity water to prepare a lithium solution with a Li2O concentration of 80g / L. After evaporation and centrifugation, the resulting wet material is dried in a vacuum at 85℃ for 1h to obtain high-purity lithium hydroxide monohydrate raw material.

[0051] (2) Material dehydration: The high-purity lithium hydroxide monohydrate raw material obtained in step (1) is heated to 450°C under a nitrogen protective atmosphere until an anhydrous lithium hydroxide raw material with a water content of <5% is formed.

[0052] (3) Nanoscale wet milling: Add anhydrous hydrazine solution to a ball mill jar with a molar ratio of Li2O: anhydrous hydrazine = 1:3. Mill the mixture in a ball mill at 500 rpm for 4 hours to obtain nanoscale anhydrous lithium hydroxide slurry.

[0053] (4) Demagnetization: High-purity sulfur powder and anhydrous hydrazine are mixed in a molar ratio of 1:3 to prepare a sulfur-containing slurry for later use. The sulfur-containing slurry and anhydrous lithium hydroxide slurry are pumped into an electromagnetic demagnetizer by a peristaltic pump for demagnetization. The magnetic field strength is set to 10000GS.

[0054] (5) Homogeneous reaction: The demagnetized sulfur-containing solution and lithium hydroxide slurry were simultaneously added dropwise to a reactor equipped with an anchor-type stirring impeller and a high-shear disperser via a peristaltic pump. The molar ratio of the feed was Li2O:S = 1:3. Under the protection of an inert atmosphere, the high-shear emulsifying disperser was turned on and the speed was set to 3000 r / min. At the same time, the stirring was turned on at 200 r / min. After reacting at 100°C for 2 hours, the temperature was increased to 300°C and the stirring speed was increased to 400 r / min. The high-shear disperser was turned off and dried for 2 hours to obtain slightly agglomerated primary particles of nano-sized high-purity lithium sulfide.

[0055] (6) Ball milling: The adhesive material is put into a ball mill and milled at a speed of 600 r / min for 1 h to obtain high-purity nano-grade lithium sulfide product. The purity data of the product is shown in Table 1.

[0056] Example 4

[0057] (1) Material purification: In a fume hood, take a 500mL bottle of commercially available hydrazine hydrate (hydrazine hydrate) and perform vacuum distillation purification to obtain high-purity hydrazine hydrate for later use; weigh 500g of lithium hydroxide monohydrate and dissolve it in high-purity water to prepare a lithium solution with a Li2O concentration of 70g / L. After evaporation and centrifugation, the resulting wet material is dried in a vacuum at 80℃ for 1h to obtain high-purity lithium hydroxide monohydrate raw material.

[0058] (2) Demagnetization: The high-purity lithium hydroxide monohydrate raw material obtained in the above steps is fed into an electromagnetic demagnetizer for demagnetization, and the magnetic field strength is set to 10000GS.

[0059] (3) Material dehydration: The high-purity lithium hydroxide monohydrate raw material obtained in step (1) is heated to 300°C under a nitrogen protective atmosphere until an anhydrous lithium hydroxide raw material with a water content of <5% is formed.

[0060] (4) Nanoscale wet milling: Add hydrazine hydrate solution to the ball mill jar, with the molar ratio of Li2O:hydrazine hydrate = 1:2. Mill in the ball mill at 600 rpm for 1 hour to obtain a uniformly dispersed nanoscale anhydrous lithium hydroxide slurry.

[0061] (5) Homogeneous reaction: High-purity sulfur powder and hydrazine hydrate were mixed in a molar ratio of 1:1 to prepare a sulfur-containing slurry for later use. The sulfur-containing slurry and lithium hydroxide slurry were simultaneously added dropwise to a reactor equipped with an anchor-type stirring impeller and a high-shear disperser via a peristaltic pump. The molar ratio of the added materials was Li2O:S = 1:2. Under the protection of an inert atmosphere, the high-shear emulsifying disperser was turned on and the speed was set to 5000 r / min. At the same time, the stirring was turned on at 300 r / min. After reacting at 150°C for 1 hour, the temperature was increased to 200°C and the stirring speed was increased to 500 r / min. The high-shear disperser was turned off and dried for 3 hours to obtain slightly agglomerated primary particles of nano-sized high-purity lithium sulfide.

[0062] (6) Ball milling: The adhesive material is put into a ball mill and milled at a speed of 600 r / min for 1 h to obtain high-purity nano-grade lithium sulfide product. The purity data of the product is shown in Table 1.

[0063] Example 5

[0064] (1) Material purification: In a fume hood, 500g of lithium hydroxide monohydrate was weighed and dissolved in high-purity water to prepare a lithium solution with a Li2O concentration of 70g / L. After evaporation and centrifugation, the resulting wet material was dried in a vacuum at 80℃ for 1h to obtain high-purity lithium hydroxide monohydrate raw material.

[0065] (2) Material dehydration: The high-purity lithium hydroxide monohydrate raw material obtained in step (1) is heated to 300°C under a nitrogen protective atmosphere until an anhydrous lithium hydroxide raw material with a water content of <5% is formed.

[0066] (3) Nanoscale wet milling: Add commercially available 4N grade hydroxylamine reducing agent to a ball mill jar, with a molar ratio of Li2O:hydroxylamine = 1:2. Mill the mixture in a ball mill at 600 rpm for 1 hour to obtain a uniformly dispersed nanoscale anhydrous lithium hydroxide slurry.

[0067] (4) Homogeneous reaction: High-purity sulfur powder and hydroxylamine were mixed in a molar ratio of 1:2 to prepare a sulfur-containing slurry for later use. The sulfur-containing slurry and lithium hydroxide slurry were simultaneously added dropwise to a reactor equipped with an anchor-type stirring impeller and a high-shear disperser via a peristaltic pump. The molar ratio of the added materials was Li2O:S = 1:2. Under the protection of an inert atmosphere, the high-shear emulsifying disperser was turned on and the speed was set to 5000 r / min. At the same time, the stirring was turned on at 300 r / min. After reacting at 150°C for 1 hour, the temperature was increased to 200°C and the stirring speed was increased to 500 r / min. The high-shear disperser was turned off and dried for 3 hours to obtain slightly agglomerated primary particles of nano-sized high-purity lithium sulfide.

[0068] (5) Ball milling: Put the adhesive material into a ball mill and ball mill it for 1 hour at a speed of 600 r / min to obtain a high-purity nano-grade lithium sulfide product.

[0069] (6) Demagnetization: The high-purity lithium sulfide after ball milling is fed into an electromagnetic demagnetizer for demagnetization. The magnetic field strength is set to 12000GS to obtain a high-purity lithium sulfide product with magnetic material less than 50ppb. The product purity data is shown in Table 1.

[0070] Comparative Example 1

[0071] (1) Material purification: In a fume hood, 500g of battery-grade lithium carbonate was weighed and dissolved in high-purity water to form a slurry, and then high-purity lithium carbonate was obtained by carbonization decomposition.

[0072] (2) Nanoscale wet milling: Add commercially available 4N grade hydroxylamine reducing agent to a ball mill jar, with a molar ratio of Li2O: anhydrous hydrazine = 1:2. Mill the mixture in a ball mill at 600 rpm for 1 hour to obtain a uniformly dispersed nanoscale high-purity lithium carbonate slurry.

[0073] (3) Homogeneous reaction: High-purity sulfur powder and hydroxylamine were mixed in a molar ratio of 1:2 to prepare a sulfur-containing slurry for later use. The sulfur-containing slurry and high-purity lithium carbonate slurry were simultaneously added dropwise to a reactor equipped with an anchor-type stirring impeller and a high-shear disperser via a peristaltic pump. The molar ratio of the added materials was Li2O:S = 1:4. Under the protection of an inert atmosphere, the high-shear emulsifying disperser was turned on and the speed was set to 5000 r / min. At the same time, the stirring was turned on at 300 r / min. After reacting at 150°C for 1 hour, the temperature was increased to 200°C and the stirring speed was increased to 500 r / min. The high-shear disperser was turned off and dried for 3 hours to obtain slightly agglomerated primary particles of nano-sized high-purity lithium sulfide.

[0074] (4) Ball milling: Put the adhesive material into a ball mill and ball mill it for 3 hours at a speed of 400 r / min to obtain a high-purity nano-grade lithium sulfide product.

[0075] (5) Demagnetization: The high-purity lithium sulfide after ball milling is fed into an electromagnetic demagnetizer for demagnetization. The magnetic field strength is set to 10000GS to obtain a high-purity lithium sulfide product with magnetic material less than 50ppb. The product purity data is shown in Table 1.

[0076] Comparative Example 2

[0077] (1) Nanoscale wet milling: High-purity lithium oxide raw material and commercially available 4N grade hydroxylamine reducing agent are added to a ball mill jar. The molar ratio of Li2O:hydroxylamine = 1:2 is used as the standard. The ball mill is run at 600 rpm for 1 hour to obtain a uniformly dispersed nanoscale high-purity lithium oxide slurry.

[0078] (2) Homogeneous reaction: High-purity sulfur powder and hydroxylamine were mixed in a molar ratio of 1:2 to prepare a sulfur-containing slurry for later use. The sulfur-containing slurry and high-purity lithium oxide slurry were simultaneously added dropwise to a reactor equipped with an anchor-type stirring impeller and a high-shear disperser by a peristaltic pump. The molar ratio of the added materials was Li2O:S = 1:3. Under the protection of an inert atmosphere, the high-shear emulsifying disperser was turned on and the speed was set to 3000 r / min. At the same time, the stirring was turned on at 300 r / min. After reacting at 150°C for 1 hour, the temperature was increased to 200°C and the stirring speed was increased to 500 r / min. The high-shear disperser was turned off and dried for 3 hours to obtain slightly agglomerated primary particles of nano-sized high-purity lithium sulfide.

[0079] (3) Ball milling: Put the adhesive material into a ball mill and ball mill it for 3 hours at a speed of 400 r / min to obtain high-purity nano-grade lithium sulfide product.

[0080] (4) Demagnetization: The high-purity lithium sulfide after ball milling is fed into an electromagnetic demagnetizer for demagnetization. The magnetic field strength is set to 12000GS to obtain a high-purity lithium sulfide product with magnetic material less than 50ppb. The product purity data is shown in Table 1.

[0081] Table 1

[0082] Sample Name purity / % Na K Ca Mg Fe Si Al Ti <![CDATA[Li2S - Example 1]]> 99.99435 0.0016 0.00057 0.000031 0.000029 0.00015 0.0026 0.00062 0.00005 <![CDATA[Li2S - Example 2]]> 99.993549 0.0017 0.00062 0.000038 0.000033 0.00019 0.0028 0.00069 0.00038 <![CDATA[Li2S - Example 3]]> 99.993033 0.0019 0.00073 0.000041 0.000046 0.00022 0.003 0.00057 0.00046 <![CDATA[Li2S - Example 4]]> 99.993138 0.0025 0.00065 0.000063 0.000039 0.00032 0.0022 0.00051 0.00058 <![CDATA[Li2S - Example 5]]> 99.991937 0.0031 0.00043 0.000055 0.000028 0.00021 0.0031 0.00048 0.00066 <![CDATA[Li2S - Example 6]]> 99.991995 0.0028 0.00054 0.000078 0.000047 0.00019 0.0032 0.00069 0.00046 <![CDATA[Li2S - Example 7]]> 99.992769 0.0035 0.00071 0.000028 0.000033 0.00024 0.0016 0.00077 0.00035

[0083] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. After reading the specification of the present invention, those skilled in the art may make some modifications or improvements based on the present invention, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A method for preparing high-purity nano-sized lithium sulfide, characterized in that... Includes the following steps: a. Material purification Purification of reducing agent: Take hydrazine hydrate, anhydrous hydrazine and / or hydroxylamine reducing agent for purification, and obtain high-purity reducing agent after removing impurities for later use; Lithium source purification: The lithium source is purified to obtain a high-purity lithium source, wherein the lithium source is battery-grade lithium hydroxide monohydrate, anhydrous lithium hydroxide, high-purity lithium oxide and / or battery-grade lithium carbonate; b. Nanoscale wet milling: Take the high-purity reducing agent and high-purity lithium source obtained in step a at a molar ratio of 1:1 to 3, mix them evenly, and obtain a high-purity lithium source slurry with nanoscale particles and uniform dispersion. c. Homogeneous reaction: Dissolve high-purity sulfur powder in the high-purity reducing agent obtained in step a to obtain sulfur-containing slurry; add the sulfur-containing slurry and the high-purity lithium source slurry obtained in step b to the reaction vessel simultaneously according to the chemical reaction stoichiometric ratio and mix them. Under the protection of an inert atmosphere, react and dry to obtain high-purity lithium sulfide with a small amount of adhesion. d. Ball milling: The high-purity lithium sulfide with a small amount of agglomeration obtained in step c is ball milled to obtain a uniformly dispersed nano-sized high-purity lithium sulfide product.

2. The method for preparing high-purity nano-sized lithium sulfide according to claim 1, characterized in that: In step a, when the lithium source is battery-grade lithium hydroxide monohydrate or anhydrous lithium hydroxide, the lithium source is dissolved in high-purity water to prepare a lithium salt solution, which is then dried and heated to decompose, to obtain anhydrous lithium hydroxide with a water weight content of <5%. When the lithium source is battery-grade lithium carbonate, it is purified by carbonization decomposition. When the lithium source is high-purity lithium oxide, purification is not required; The lithium source mentioned in step a, if battery-grade lithium hydroxide monohydrate or anhydrous lithium hydroxide is used as raw material, then the concentration of the lithium salt solution is Li2O: 60-80 g / L, and the drying method is vacuum low-temperature drying at a temperature of 75-90℃; if battery-grade lithium carbonate is used as raw material, then water is added to prepare a slurry, and then it is purified again by carbonization decomposition; if high-purity lithium oxide is used as raw material, no purification is required.

3. The method for preparing high-purity nano-sized lithium sulfide according to claim 1, characterized in that: The mixing method in step b is as follows: wet milling with a ball mill for 1 to 8 hours at a speed of 300 to 600 rpm.

4. The method for preparing high-purity nano-sized lithium sulfide according to claim 1, characterized in that: In step c, when the reducing agent is hydrazine hydrate and / or anhydrous hydrazine, high-purity sulfur powder is mixed with it at a molar ratio of 1:1 to 3 to prepare a sulfur-containing solution. When the reducing agent is hydroxylamine, high-purity sulfur powder and hydroxylamine are mixed at a molar ratio of 1:2 to 4 to prepare a sulfur-containing solution. The molar ratio of high-purity lithium source slurry to sulfur-containing solution is Li2O:S = 1:1 to 3.

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